Dynamic Microdomains in Brain Extracellular Space

大脑细胞外空间的动态微域

• 批准号: 7333053
• 负责人: SABINA HRABETOVA
• 金额: $ 14.95万
• 依托单位: SUNY DOWNSTATE MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2009-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7333053
• 关键词: biological transport; brain morphology; brain stem; cerebellum; charge coupled device camera; computer simulation; diffusion; electron microscopy; extracellular; fluorescent dye /probe; glia; hypothalamus; ionophores; laboratory rat; macromolecule; neocortex; neurophysiology; neuroregulation; nontherapeutic iontophoresis; quaternary ammonium compound; tissue /cell culture

DESCRIPTION (provided by applicant): In brain, intercellular communication, nutrient and metabolite trafficking, and the delivery of drugs takes place in the extracellular space (ECS). Diffusion, the major transport mechanism mediating these processes, is governed by two structural parameters of the ECS, tortuosity and volume fraction. The tortuosity (?) represents the hindrance imposed on the diffusing molecules by the tissue in comparison with an obstacle-free medium, whereas the volume fraction (a) is the proportion of tissue volume occupied by the ECS. A fundamental question remains unanswered: what hinders molecules traveling through the brain? In healthy brain, ? extracted from the diffusion of small ECS markers is about 1.6 but increases to 1.9 in pathologies where cells swell. It had been thought that ? can be explained by circumnavigation of markers around cells. However, ? derived theoretically or obtained from simulations in media composed of convex cells exhibits an upper limit of about 1.23. Obviously, some other significant factor determines ? in the brain. The central hypothesis of this proposal is that the ECS contains pocket-like microdomains that can significantly slow down the diffusion process, and that these microdomains are formed and regulated by glia. The iontophoresis-based tetramethylammonium (TMA) method and integrative optical imaging (IOI) will quantify diffusion of TMA+ and fluorescent macromolecules, respectively. Rat neocortical slices will be the main preparation but some experiments will examine the cerebellum, hypothalamus or brainstem because of the unique morphological features of these regions. There are three specific aims. Aim 1. Establish that pocket-like microdomains hinder diffusion in brain ECS. The ECS structure will be altered by background macromolecules that fill the pockets and ? will be measured. Trapping of macromolecules will be characterized by the IOI and electron microscopy will localize the entrapment sites. Aim 2. Show that glia form and regulate microdomains. Tortuosity will be measured in the cerebellum where glial wrappings are abundant, in the hypothalamus where withdrawal of glial processes from the supraoptic nucleus will be induced pharmacologically, and in the neocortex where glial toxins will swell glia. Aim 3. Measure diffusion within a microdomain. Diffusion will be measured within a microdomain model, the giant calyx of Held synapse in the brainstem. Computer simulations of diffusion will complement experimental work on Aims 1 and 3. This proposal is focused on basic research with major implications for transport of substances in the nervous system. It identifies a novel role for glia in regulation of diffusion in the ECS.

描述（由申请人提供）：在大脑中，细胞间通讯，营养和代谢物运输以及药物递送发生在细胞外空间（ECS）。扩散是介导这些过程的主要输运机制，它受ECS的两个结构参数——挠度和体积分数的控制。弯曲度（?）表示与无障碍介质相比，组织对扩散分子施加的阻碍，而体积分数(a)是ECS占据组织体积的比例。一个基本问题仍未得到解答：是什么阻碍了分子在大脑中穿行？在健康的大脑中？从小的ECS标记物的扩散中提取约为1.6，但在细胞肿胀的病理中增加到1.9。人们曾经这样想过吗？可以通过细胞周围的标记来解释。然而,?从理论上推导或从由凸胞组成的介质中模拟得到，其上限约为1.23。显然，还有其他一些重要因素决定了？在大脑里。该研究的核心假设是，ECS中含有可以显著减缓扩散过程的口袋状微结构域，这些微结构域由胶质细胞形成和调节。